[bug#60962] [PATCH v3] tests: Fix implicit function declaration in ax/depcomp.sh

[Karl Berry]

Hi Frédéric,

     [in t/ax/depcomp.sh]
     - Replace the mv operation by a cp operation to ensure that subfoo.h is
       considered being modified.

Thanks for the clear explanation and simple patch :). I (finally)
installed it, just adding a comment, so am closing this. Happy hacking,
Karl